/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.logging;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * FIFO Circular List.
 * 
 * Once the size is reached, it will overwrite previous entries
 * 
 */
public class CircularList<T> implements Iterable<T> {
	private T[] data;
	private int head = 0;
	private int tail = 0;
	private int size = 0;

	@SuppressWarnings("unchecked")
	public CircularList(int size) {
		data = (T[]) new Object[size];
	}

	@SuppressWarnings("unchecked")
	public synchronized void resize(int newsize) {
		if (newsize == this.size)
			return;

		T[] vals = (T[]) new Object[newsize];
		int i = 0;
		if (newsize > size) {
			for (i = 0; i < size; i++) {
				vals[i] = data[convert(i)];
			}
		} else {
			int off = size - newsize;
			for (i = 0; i < newsize; i++) {
				vals[i] = data[convert(i + off)];
			}
		}
		data = vals;
		head = 0;
		tail = i;
	}

	private int convert(int index) {
		return (index + head) % data.length;
	}

	public boolean isEmpty() {
		return head == tail; // or size == 0
	}

	public int size() {
		return size;
	}

	public int getBufferSize() {
		return data.length;
	}

	private void checkIndex(int index) {
		if (index >= size || index < 0)
			throw new IndexOutOfBoundsException("Index: " + index + ", Size: "
					+ size);
	}

	public T get(int index) {
		checkIndex(index);
		return data[convert(index)];
	}

	public synchronized void add(T o) {
		data[tail] = o;
		tail = (tail + 1) % data.length;
		if (size == data.length) {
			head = (head + 1) % data.length;
		}
		size++;
		if (size > data.length) {
			size = data.length;
		}
	}

	public synchronized void clear() {
		for (int i = 0; i < data.length; i++) {
			data[i] = null; // for GC
		}
		head = tail = size = 0;
	}

	public List<T> toList() {
		ArrayList<T> list = new ArrayList<T>(size);
		for (int i = 0; i < size; i++) {
			list.add(data[convert(i)]);
		}
		return list;
	}

	@Override
	public String toString() {
		StringBuilder str = new StringBuilder();
		str.append("[");
		for (int i = 0; i < size; i++) {
			if (i > 0) {
				str.append(",");
			}
			str.append(data[convert(i)]);
		}
		str.append("]");
		return str.toString();
	}

	@Override
	public Iterator<T> iterator() {
		return new Iterator<T>() {
			int idx = 0;

			@Override
			public boolean hasNext() {
				return idx < size;
			}

			@Override
			public T next() {
				return get(idx++);
			}

			@Override
			public void remove() {
				throw new UnsupportedOperationException();
			}
		};
	}
}
